The goal of this study is to determine the role of cytokines in acute graft-versus-host disease (GVHD) following human marrow transplantation. Acute GVHD is a serious complication that kills roughly one-fourth of the 30-50% of patients who develop it. Furthermore, acute GVHD predisposes to the development of chronic GVHD, another major posttransplant complication. Knowledge of the relationship of patient TNF levels to GVHD will be used to improve early diagnosis and to develop preventive and early intervention therapies that are based on TNF neutralization. Preliminary studies have shown that 1) the presence of serum tumor necrosis factor alpha (TNF) and acute GVHD correlate and that 2) TNF inhibits basal keratinocyte proliferation. Specific aims of this study test the hypothesis that cutaneous GVHD is caused by the cytostatic action of TNF on basal keratinocytes. The aims ask the following questions. 1) Can pilot data linking serum TNF to GVHD can be confirmed? 2) Do serum TNF levels increase before or after clinical GVHD? Do they predict GVHD? 3) Do serum TNF levels predict or parallel GVHD severity? 4) Do serum TNF levels predict the outcome of GVHD treatment? 5) Are serum TNF levels linked to infection/gut contamination? 6) Does serum TNF correlate with known GVHD risk factors? 7) Is TNF in patient sera cytostatic for basal keratinocytes in vitro? 8) Is keratinocyte growth inhibited by cutaneous GVHD? 9) Do infiltrating lymphocytes inhibit keratinocyte growth? Immuno- and bioassays will be used to assess levels of TNF in serial serum samples drawn 7 to 35 days after marrow transplantation. These results and selected clinical data will be stored in a computerized database and analyzed statistically to answer questions 1-6. Sera and TNF at levels measured therein will be tested for their cytostatic/cytopathic effects in vitro to answer question 7. Evidence that GVHD leads to cytostasis (question 8) will be sought by determining the cell-cycle profiles of keratinocytes in epidermal biopsies. Finally, local tissue levels of TNF will be assessed in freshly isolated epidermal blister fluids and skin-infiltrating cells. The same patient sera and experimental approach can be used to analyze the role of other effector cytokines, such as IF-gamma and lymphotoxin, in acute GVHD.